1. Technical Field
The present invention relates to a stator coil unit for rotary electric machines such as electric motors and electric generators, and in particular, to a concentrated-winding type stator coil unit for the rotary electric machines.
2. Related Art
In a rotary electric machine, a stator is required to convert electric energy into kinetic energy or vise versa. At present, there have been various types of stators.
One type of stator has coils each wound around each of teeth (serving as magnetic poles) of a stator core in a concentrated manner and the wound coils (frequently referred to as tooth coils) are, phase by phase, mutually connected with each other to form each phase coil. Such a stator is called “concentrated-winding type stator.” In winding a coil around each tooth to manufacture the concentrated-winding type stator, it is general to employ an assembled type of core, in which partial cores divided teeth by teeth are assembled to form a stator core.
If the stator core is designed as an outer rotor type of stator, a cylindrical stator core can be used, in which a coil is directly wound around each of the teeth protruding from the outer circumferential surface of a cylindrical stator core. Alternatively, an inner rotor type of stator might be used, in which a coil is directly wound around each of the teeth protruding from the inner circumferential surface of a cylindrical stator core. A Japanese patent laid-open publication No. 2001-25198 (reference 1) discloses this kind of concentrated-winding type stator.
As shown by the reference 1, in the concentrated-winding type stator, the tooth coil is wound around each tooth or each bobbin loaded on each tooth by a necessary number of turns. Like the normal coil winding, the coil is wound in turn in the axial direction of each tooth. As a result, mutually neighboring two turns, which are electrically connected with each other, can be wound at the highest density if the two turns are placed without a gap along the circumferential surface along its axial direction.
Like the normal coil winding, the wound coil starts at one end of each tooth in a radial direction thereof (normally, the base portion of each tooth) and reaches the tip portion of the teeth, so that the first layer of coil (hereinafter called “the first layered coil” as well) is constituted. The coil is then wound on the first layer coil such that the coil returns from the tip portion of each tooth to the base portion thereof, thus constituting the second layer of coil (hereinafter called “the second layered coil” as well). Likewise, the coil is wound on the second layered coil to form the third layered coil, thereby providing a high-density winding manner. The first, second and third layered coils and subsequent coils are generalized as “layered coils.”
A Japanese patent laid-open publication No. 2001-186703 (reference 2) discloses two winding ways: one is that the beginning end of a tooth coil is placed at the basis portion (or the tip portion) of each tooth and the dead end of the tooth coil is placed at the tip portion (or the base portion), while the other way is that both the beginning and dead ends of a tooth coil are placed at the tip portion of each tooth. In this case, the number of layered coils is two, so that the two-layered coil is formed.
However, as stated above, crossover wires are used to mutually and sequentially connect the tooth coils located at predetermined pitches in the circumferential direction of a stator, with the result that each phase coil is configured. Accordingly, in the two-layered coil type of tooth coil taught by the reference 2, it is probable that both the beginning and dead ends of the tooth coil be localized at the tip. In such a localized location of both the ends, the crossover wires are located to almost touch the surface of the rotor, if the crossover wires are bridged to be the shortest. It has been found that this bridging location has various drawbacks. For example, vibration will cause the wire to touch the rotor and the wire obstructs fitting work of the rotor into a machine.
One solution to those drawbacks is provided by a particular connection manner, in which the crossover wire is drawn from the dead end located at the tip portion of each tooth to the base portion thereof in the radial direction of a rotor (in the case of the inner rotor type, to each radial outside end), is made to extend along the rotor surface to reach the next tooth belonging to the same phase, and is made to extend along the tooth to arrive at the tip portion thereof. The crossover wire, which has been at the tip portion of the next tooth, is connected to the beginning end of a tooth coil wound around the tooth and located at the tip portion. However, this kind of connection manner will cause the crossover wire to be longer between teeth, thus leading to an increase in power loss on account of resistance across the stator coil.
In addition, the winding technique taught by the reference 2 involves a folded portion, at which the wire is folded from the first layer coil to the second layered coil so as to allow both of the last turn of the first layered coil and the first turn of the second layered coil to be stacked one on the other. At this folded portion, the wound coil becomes thicker and protrudes from the surface of a tooth in the radial direction thereof by an amount corresponding to the thickness (of diameter) of the wire. This protrusion of the wound coil will reduce a slot lamination factor. That is, to make it possible to wind one pair of tooth coils around two teeth respectively located at both ends of one slot, an excessive space should be secured to accommodate the respective folded portions therein due to the protrusions of the folded coil in the radial direction. Therefore, of a circumferential width of each slot, a space corresponding to a width which is two times the thickness of the wire becomes useless, reducing the slot lamination factor.
Although the above has been explained on condition that the tooth coils are mutually connected in series phase by phase, the foregoing difficulties are true of a stator coil unit in which the tooth coils are mutually connected in parallel phase by phase with the use of crossover bus bars.